Electron tube



NW. 17, 1959 E. LABIN 2,913,620

ELECTRON TUBE Filed July 19, 1954 3 Sheets-Sheet 1 v 2 1 V, 4 a l DIRECTION or 5 MAG/V5770 new FIG. 2

OUTPUT l H 19 18 l l i j/ 15 T .4 El/A can rm EV/760A TED EAVELOPE ENVELOPE P FIG-3.4 FIGS Edouara/ L in B a galln ATT RN Y Nov. 17, 1959 E. LABIN 2,913,620

ELECTRON TUBE Filed July 19, 1954 3 Sheets-Sheet 2 usexnvs ems NEGATIVE BIAS so 1 2s\ 7 coumm. nee-rm: CONTROL nan-r 31 V I I I v I 26 I A?! I r I- 0L ELECTRODE 51 4804 TED F; l A/MELOPE V /L'/42 Edouard LaLin FIG.

7 B, awn nwwa ATTORNEY Nov. 17, 1959 LABlN 2,913,620

ELECTRON TUBE ined July 19. 1954 a Sheets-Sheet. s

ELECTRON TUBE Edouard Labin, Paris, France, assignor to Societe Nouvelle (1e lOutillage RBJV. et de La Radio-Industrie, Paris, France, a corporation Application July 19, 1954, Serial No. 444,240

Claims priority, application France July 24, 1953 6 Claims. (Cl. 315- 12) This invention relates to an electron tube for producing an output signal, particularly a current, which varies according to a predetermined law expressed in terms of one or more independent variables, which may be the control voltages applied to the tube.

Electronic devices have already been proposed for producing an output signal f(x) in response to an input signal x. Such devices may be called electronic operators, since they apply an operator f to a variable x to' transform the variable into a function f(x). Such electronic devices may be in the form of a vacuum tube provided with a beam shaping assembly designed to impose a desired transformation upon a uniform density electron beam. The unmodulated beam passes through an electron optical system including a control electrode or deflecting grid which deflects the beam proportionately to the input signal x onto a split collector electrode shaped to intercept a fraction of the beam which varies with its position.

An arrangement of the type described above has certain important defects. It requires an accurate shaping of the electron beam, which can only be obtained by precise electron optical structures, highly stabilized voltages, and very small currents. Further, the electron optical system requires relatively high deflecting voltages, because of the low deflection sensitivity of the high speed electrons, and on the other hand satisfactory operation is not obtained with slow electrons.

It has also been proposed to realize electronic operators or transformation devices by means of a cathode ray tube having an opaque mask in front of its fluorescent screen. The mask is formed so that the fraction of the light transmitted to a photocell, when the beam is deflected in accordance with the variable signal x, corresponds to a function f(x). This system has the advantage that various functions f(x) can be obtained by using different masks. However, the system is complex and its overall efficiency is very low.

It is an object of the invention to overcome the principal disadvantages of the prior system by providing a system which adds the advantages of the two cited prior art systems, that is to say in which the transformation is entirely performed inside a tube envelope and in which it is possible to obtain an output signal which is a function of two independent variables of the type where x and y are the two variables.

It-is another object of the invention to provide an electron tube device which delivers an output current of the same order of magnitude as an ordinary amplifying receiving tube in which said output current is a function ;f(x) of the input signal x or the product f(x) -g(y) of two functions of two independent input signals x and y.

It is another object of the invention to provide a tube of the kind referred to above in which the form of the function f or of the functions f and g are changed by 2,913,620 Patented Nov. 17, 1959 changing the shape of the electron emissive coating on the cathode of the electron gun inside the tube.

It is another object of the invention to provide tubes of the kind referred to above which do not require any high precision mechanical parts or mounting.

It is another object of the invention to provide tubes of the kind referred to above which are easily reproduceable.

A principal feature of the present invention is that an electron tube is provided wherein the cathode itself acts as the beam shaping element. The emitting area of the cathode may be delimited by a plurality of open or closed outlines determined in a manner to be explained later. The independent variable or input signal control, an aperture or shutter so as to vary its size or to cause it to scan the emitting surface of the cathode so as to vary the effective portion of the emitting surface in accordance with the input signal.

Thus the variation of the beam current occurs at the cathode surface, by the control of very slow electrons.

According to another aspect of the invention, the actual cathode is transposed to form a virtual cathode on a plane having an opening of a given shape. The velocity of the electrons in the virtual cathode is as low as in the actual cathode. According to one embodiment of the invention, the slow electrons are transferred by means of a magnetic field which reflects part of the electrons back toward the cathode. The current density from the actual cathode is varied according to the magnetic field, which thus acts as a first control means, in response to a first independent variable. An electron optical system enables the selection of a particular part of the transferred cathode and thus permits a second control in accordance with a second independent variable.

According to another feature of the invention the cathode may be symmetrical. Also, the cathode may be a closed structure, except for the shaped apertures in the plane or planes of one or more transferred cathodes.

According to another feature of the invention the infiuence of the tube load circuit is reduced by the use of an electron multiplier between the load and the electron beam target.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following description with reference to the drawing, in which:

Figure 1 is a schematic diagram showing how the electrical field acts upon the electrons emitted by a thermionic cathode;

Figure 2 shows the influence of a magnetic field upon low velocity electrons as emitted by a cathode, and the resulting transfer of the cathode;

Figures 3A and 3B represent two embodiments of cathodes, the emitting surfaces of which are specially shaped according to the invention;

Figures 4 and 5 are schematic diagrams of vacuum tubes according to the invention;

Figure 6 shows another electron tube according to the invention;

Figure 7 shows a tube, which is able to deliver an output signal which is a function of two independent variables;

Figure 8 is a schematic illustration of an electron tube according to Figure 1;

Figure 9 illustrates an electron tube in accordance with Figure 6;

Figures 10-12 are partial views showing grid and cathode arrangements.

In Figure 1 there is shown a three-electrode electron gun or tube comprising an emitting cathode 1, the surface of which is coated with an emitting material, a grid structure having an axial opening 3 and an anode 4. Voltage values at which these different electrodes are maintained with respect to'potential V of the cathode, are arbitrarily fixed. The grid potential is sli'ghtly negative volts for instance) and the anode potential is positive (100 volts for instance).

Equipotential surfaces resulting from the establish ment of the electrical field in this structure have been represented in full lines. It must'be clearlyunderstood that the shape of the equipotential surfaces depends essentially on the geometry of the structure and that Figure 1 shows the usual field in ordinary triode electron guns when the spacing between grid and cathode is about 1 mm., that between grid and plate is about 10 mm. and the diameter of the aperture 3 is about 0.1 mm.

The Zero equipotential surface has been represented in interrupted lines. The zero equipotential surface cuts the cathode plane along an outline which defines a surface which is represented by lines 13, 13' in Figure 3A tube cut-off voltage, the zero equipotential surface intersectsl effectively the cathode plane. When the grid is made more negative than said cut-off voltage, the whole emitting plane is in the region of negative voltage. In order that the electrons emitted by the cathode may reach the anode, generally speaking, they must be attracted towards it immediately after. they have been delivered by the emitting surface. That is, only the electrons emitted from the part where the electronic field is directed from the-cathode towards the anode 4 are able to leave the emitting surface and to follow the field lines toward the anode. Electrons emitted from other points of the cathode are subjected to a field which repels them in the opposite direction, which means that they cannot leave the emitting surface. In prior art electron guns, the modulation o-f'the electron beam current is obtained by varying the area of the cathodic surface from which the electrons can escape, by deformation' of the zero equipotential surface; in other Words,

the voltage of grid 2 or rather the ratio of the gridvoltage 2 to that of the anode which is generally fixed is altered. Modulation of the electron beam current according to a characteristic controlled only by the geometry of the gun structure is thus obtained.

According to the present invention, the modulation characteristic of the beam current is adjusted to the desired form by using a cathode 1, the emissive surface of which is carefully defined by one or a plurality of outlines which are preset on the cathode surface, as later explained,'instead of using an emitting surface which is symmetrical with respect to the electron gun axis.

. 2,913,eao I p a 7 shown at 6 in Figure 2. This image acts as the trans- Figure 2 shows the action of a magnetic field 5 upon electrons delivered by a cathode surface 1, when the field is parallel to the cathode plane. As is well known, the electrons are emitted with initial velocities the direction and absolute magnitude of which are a complex function of many parameters and depend on the cathode structure and the operating temperature. It is possible to show that a magnetic field acts according to Lorentz law when applied to thermoelectrons, the space charge being approximately without any effect. Thus, the electrons emitted by the cathode will follow circular paths 8, 9 depending upon the orientation of the initial veloc- V ity and its magnitude; it is also possible to show that ferred cathode or the virtual cathode and the magnitude of the electron velocities is not changed since a constant magnetic field does not accelerate electrons.

it is evident from Fi ure 2 that instead of using an actual cathode having a predetermined distribution of emissivity on its active surface to provide an electron emitter having a predetermined density distribution, a cathode assembly may be used comprising a uniform electron emitting portion and a predetermined opening in the same plane; As explained above, for a particular cathode assembly 'of the type represented in Figure 2 the electron density in the opening will depend only on the magnitude of the magnetic field, which may'vary in accordance with an input signal and thus introduce control in accordance with a first independent variable.

Figures 3A and 3B show two examples of emitting structures according to the invention, which may form the cathode 1 of Figure 1. Figure 3A shows a diskshaped plane cathode consisting of a non-emissive sup port 11) upon which an emissive coating 11 is deposited on the area outlined by lines 12. The intersection of the cathode plane with the zero equipotential surface is indicated by the line 13, shown as circular and concen tric with the disk. The area of the emitting surface varies with the radius according to a law determined by outline 1212. This law is the modulation characteristic of the electron beam current.

Figure 3B shows a cathode which may be cylindrical, having axis 14. Such a cylindrical cathode may be used in the tube shown in Figure 1, or in Figure 5 which will'be described hereinafter. When used in an electron gun or tube of the type shown in Figure 1, it will be understood that the grid 2 and anode 4, shown only schematically in Figure 1, would be cylinders concentric with the cathode, as is common in electron tubes. Cylindrical grids surrounding the cathode are shown in Figures 10 and 11. The non-emitting body 10' of the cathode has an emitting portion 11 between the lines 12'-12'. The actual emitting portion of the cathode will be the portion of area 11 which lies between the zero equipotential lines 13. The parallel equipotential lines 13 may be produced obviously by an elongated slot in the cylindrical grid'which is parallel to the axis 14.

To obtain a given modulation characteristic, it is necessary to determine the corresponding outline 12 which defines the emitting portion of the cathode. To do so, it is necessary to 'know the geometrical data of the electron gun, which for a given type'of tube, are obtainable experimentally. When these data are known, calculation gives the equation of outline 12 for each desired modulation characteristic f(x). For all the tubes made of identical constituent units, an electronic operator or transformation generator may be obtained the characterrstic of which is only fixed by the outline of the cathode emissive coating, all the other parts of the tube being identical. 7

After determination of the outline 12, it iseasy to formthe cathode by means of any one of the coating processes known per se. Some of these processes will be mentioned. For instance, the whole surface of the cathode may be coated with the emissive substance, the part which is outside the outline 12 being removed by mechanical or chemical process. The emissive substance may also be deposited by cataphoresis through the aperture of a mask laid upon the holder surface, this aper ture being shaped according to the desired outline. 'The same mask maybe used and the emissive coating may be sprayed on thecathode.

According to another process, the desired outline may be cut from an uniformly emissive surface and the piece thus obtained may be directly used as a cathodic structure or fixed on a non-emissive holder. Direct utilization of the cut piece as a cathode is advantageous to avoid the heating of non-emissive parts of. a cathodic structure. However, this solution is not always possible, owing to mechanical conditions.

An electron tube having a cathode according to the invention is schematically shown in Figure 4. This tube comprises a cathode 15 having emissive portions 15' and heated by heater 16, a modulation grid 17 and an anode 18. Anode 18 is a target with a secondary emission ratio higher than one. Secondary electrons are collected by anode 19 which is maintained at a potential slightly higher than that of target anode 18, and acts as does anode 4 of the electron gun on Figure 1.

Utilization of secondary emission target 18, while not essential to the invention, makes an accurate determination of the tube parameters easier, owing to the fact that it provides a buffer or decoupling action between the output circuit, connected to the collector electrode 19, and the electron beam. When the load is connected directly to anode 18, the voltage ofthe anode varies according to the voltage drop across the load impedance. Yet, as said above, one of the parameters of the tube is the ratio of anode to grid voltage. Utilization of a secondary emission stage secures a greater steadiness for this parameter under working conditions. It is desirable also to use a stabilized anode supply voltage and an electrode arrangement which prevents any interaction between the field established between electrodes 18 and 19 and the field between grid 17 and cathode 15.

The tube illustrated in Figure 5 is similar to that of Figure 4 and the same reference numerals are used in both figures to designate corresponding parts. In Figure 5, however, the electrode arrangement is symmetrical, as is apparent. It will be obvious that such a symmetrical arrangement can be achieved by. making the electrodes on one side of the tube duplicates of those on the other side, or by making the electrodes themselves symmetrical, as, for example, cylindrical. Since the tube of Figure 5 functions in the same manner as that of Figure 4, a detailed description thereof is unnecessary.

In all the embodiments described so far the portion of the emissive area utilized increases with grid voltage. This means that an increase in input signal causes an increase in the output signal, unless the output signal remains constant. In other words, the above described embodiments perform a monotonic transformation or operation.

In order to obtain a transformation according to a function which has maxima and minima, it is possible to use the diiference between two monotonic functions obmatically shown on Figure 6. The diagrammatic representation of Figure 6 is similar to that of Figure 1. As shown, the modulation grid is made up of two parts 2 and 2' electrically insulated from each other and maintained at diiferent D.C. voltage (-10 v. and 6 v.), The input signal being applied to them by an input circuit 2" in a differential manner. A deformation of the zero equipotential surface is thus obtained, as shown by the interrupted lines in Figure 6. The intersection 13 of this equipotential surface with the cathode plane is no longer symmetrical with respect to the axis of the tube and, with a suitable adjustment of the grid D.C. voltages, the emissive area may be reduced to a small strip which is shifted along the cathode when the control signal is varied. A moving laminar beam is thus obtained. The beam shaping is accomplished directly at the cathode and without any action 'of an electron optical system upon an already formed beam. By shaping the emitting surface of the cathode according to a properly determined contour, it will be apparent that a non-monotonic function of the control signal may be obtained.

In Figure 7 isshown an embodiment of the invention which delivers an output signal which is a function of two independent variables of the separate variable type. This embodiment incorporates a virtual cathode such as shown at 6 in Figure 2. The cathode structure is a nearly closed box 20 comprising two apertures 21 and 22 through which electrons, which are emitted by emissive surfaces 23 and 24 set on the inside walls of box 20, may escape. Each aperture is set substantially in the same plane as the associated emissive surface and acts as a properly shaped aperture, such as aperture 6 of Figure The virtual cathodes at 21 and 22 are obtained by transferring the electrons emitted by surfaces 23 and 24 by means of a magnetic field 25 parallel to the emissive surfaces 23 and 24. The magnetic field 25 is obtained by means of a current corresponding to the input signal which flows through coils 26. Electrodes 27, 28,

29 and 30 act as modulating grids such as 2 and 2 with respect to the slow electrons arriving in the plane of apertures 21 and 22. Collecting anodes are shown as 31 and 32 for each of the cathodes. Of course if monotonic functions only are to be obtained, insulated electrodes 27, 28 and 29, 30 respectively may consist in a unitary control grid with a suitable hole as shown on Figure 1. It will be understood, of course, that a nonsymmetrical structure may be used, i.e. having only one emissive surface associated with one aperture and one collecting anode, instead of the symmetrical or dual structure shown in Figure 7.

As has been said above, the density of electrons at a given point of one of the apertures 21 and 22 in a given tube is a function only of the magnetic field intensity 25. The output signal appearing on plates 31 and 32 is a function of the magnetic field value determined by the structural constants of the cathodic structure and by the shape of apertures 21 and 22, when no control voltage is applied to the modulating grids.

A second control which is independent of the magnetic field 25 may be used to choose the active parts on the surface of the apertures 21 and 22. This second control may be effected by applying said second independent variable as a control voltage to grids 27 to 30. Each pair of grids is fed differentially. Thus the output current collected by 31 and 32 may be made to be a function of two independent variables. The travel of the electrons from cathodes 23 and 24 to apertures 21 and 22 and thence to the collector electrodes 31--32 indicated by arrows.

The cathode assembly shown in Figure 7 may be used as the cathode of the tubes shown in Figures 4 and 5, the cathode assembly being provided with only one aperture for use in Figure 4 and with two apertures for the tube of Figure 5. Electrodes 27-30 may serve as the input electrodes, in which case the input signals will be impressed on or between pairs of these electrodes in the same manner as in Figures 1, 4, 5 or 6.

It will be evident that the cathode illustrated in Figure 7 is merely exemplary and that many variations from the structure as illustrated may be adopted. The cathodes 23 and 24 may take many other forms,. The emissive area may be much larger than shown and even the entire interior of body 20 may be coated with emissive material. Well known means may be used in the cathode assembly 20 for electrically focusing or concentrating the electrons on the apertures, in addition to the magnetic field. It is possible also to use cathodes of other known types, such as storage cathodes, or photoelectric or secondary emission cathodes, in addition to the types herein described. While, for the sake of simplicity, the tubes described herein are of the triode type, it is apparent that the invention is applicable to other known tube types, such as tetrodes and pentodes.

It is obvious that the magnetic field 25 of Figure 7 should satisfy certain conditions and, especially, it should be free of aberrant magnetic fields. However, a direct current field may be superimposedon ithesignal controlled magnetic field for concentrating the electrons on the apertures. 1 I

An electron tube according to myinvention may have a form similar to conventionaltubes, for example, as shown in Fig. 8. Herein the tube has a base 40, terminal pins 41 and an evacuated'envelope 42. The grid 2 is cylindrical and has an aperture 3.. Cathode 1 is provided with a heater 16 and has an emissive surface 11. of the form, for example, shown in Fig. 3A. V

Fig. 9 shows a tube similar to that of Fig. 8fexcept that the grid consists of two insulated portions 2, 2' separated by an insulator4l4, a portion 45 of which separates the two halves 46 and 47 of the 'end face of the grid. The grid 2, 2 may be connected as shown in Fig. 6. j V I Fig. 10 shows a cathode 1 of the form illustrated in Fig. 3B. The emissive portion of the cathode isbounded by the lines 12. The grid 2 has an opening 3'-juxtaposed to the emissive portion 'of the cathode Fig. 11 shows a grid and cathode structure similar to that of Fig. 10 except that the grid consists'of portions 2, 2' separated by an insulator 48. The grid of Fig. 11 is thus adapted to be connected to the input circuit as shown in Fig. 6. p

, Fig. 12'shows a cathode 1 of the form shown in Fig. 3A. Grid 2, 2' is of the form shown in Fig. 6 and includes an insulator 49 which separates the grid into its two halves 2, 2'. The end face of the grid is provided with a diametrical slot 3, so that a laminar electron beam 7 produced. If the insulator 49 is omitted, and the grid is formed of one complete cylinder, the structure will function similarly to that of Fig. 8. 7

Since many variations and alternatives, such as those mentioned above, will be recognized as being applicable to the present invention by persons skilled in this art, the

invention is not intended to be limited except as defined in the following claims.

What I claim is: 7

1. An electron tube device for producing an output current whose instantaneous magnitude varies as a given mathematical function of the instantaneous value of a variable input signal, comprising an emissive cathode, means including said cathode for producing a stream of low-velocity electrons emerging from a surface having an outlinewhich is related to said mathematical function, control means adapted toreceive said input signal and anode means for producing jointly with said control means a variable electron-accelerating field terminating at said surface, thereby generating an electron current of a magnitude representing said mathematical function of the value of the input signal.

2. An electron tube device for producing an output current whose instantaneous magnitude varies as a given mathematicalfunctionj of the instantaneous value of a variable input signal, comprising a plane cathode member having an electron-emissive surface and an aperture spaced from and co-planar with said surface; said aperture having an outline which is re'lated'to said mathematical function, magnetic-field-producing means for producing a stream of low-velocity electrons emerging from one side of said' aperture by focusing emitted electrons from said surface upon the other side of said aperture, control means adapted to receive said input signal and anode means for producing jointly with said control means a variable electron-accelerating field terminating at said one side of said aperture, thereby generating an electron current of a magnitude representing said mathematical function of the value of the input signal.

3. An electron tube device according to claim 1, wherein said. cathode includes a cylindrical sleeve having an electron emissive coating on the end Wall thereof, said coating having an outline related to said mathematical function, said control means including a cylindrical sleeve surrounding the first mentioned sleeve and having an aperture in one end wall thereof facing said coating, said anode means being parallel to said end walls of said cylinders. V v l 4. An electron tube device according to claim 1, wherein said cathode includes a plate having an electron emissive coating thereon, the outline of said coating being related to said mathematical function, said control means comprising a pair of plates insulated from each other and spaced from each other to provide an aperture ther between in juxtaposition to said electron emissive coating. 7 5. An electron tube device according to claim 1-, wherein said cathode is inthe form of a cylinder having an electron emissive coating on the outer cylindrical wall thereof, the outline of said coating being related to said mathematical function, said control means including a conductive cylinder having a slot in juxtaposition to said coating. v

6. An electron tube device according to claim 1, wherein said control means. is adaptedto vary the extent of the electron-accelerating field across said surfacein response to'the magnitude-of the input signal.

6 References Cited in the file of this patent UNITED STATES PATENTS.

Roosenstein etal. Dec. 12, 1939 McNaney May 19, 1942 Labin et a1. Mar. 30, 1948 Steele No'v.'14, 1950 Rabinovitch Aug. 14, 1951 Dodds Jan; 1, 1952 Pay Nov. 11, 1952 Szegho et al. Jan; 26, 1954 

